This invention relates generally to the art of packaging films and more particularly to films useful in the packaging of food products.
It is common practice in packaging many goods, including food items, to use what is generally known as form-fill-seal equipment. In the vertical form-fill-seal arrangement, flexible packaging material is fed from a rollstock to a tube former where a tube is fashioned from the sheet material into a vertically dependent, upwardly open tube having overlapping longitudinal edges. These overlapping edges are subsequently sealed together longitudinally by means well known in the art and the end of the tube is sealed together by a pair of transverse heat seals which are vertically spaced apart. At this point the tube is filled with a measured quantity of the product to be packaged. A second heat sealing operation, typically performed after the filled tube has been downwardly advanced, completes enclosure of the product. Simultaneously with or shortly after the transverse heat sealing step the tube is completely transversely severed by known cutting means in a space between the vertically spaced apart pair of transverse heat seals. Thereafter the tube is downwardly advanced and the cycle is successively repeated so as to form a multiplicity of individually packaged products.
Alternatively, a single transverse heat seal including a pair of horizontally spaced apart sealing jaws may be used to form in effect two vertically adjacent heat seals which are simultaneously or subsequently severed at a line vertically intermediate the heat seals.
Flexible packaging material useful for this as well as other applications typically must meet stringent requirements imposed by the particular food or other article to be packaged. In some cases, for example in high acid foods such as tomato paste and other tomato products, the package must be capable of adequately protecting the food item after packaging and through the distribution cycle until the packaged product reaches the end user at point of sale.
Additionally, products such as those described above are sometimes introduced into the formed tube at relatively high temperatures of about 200.degree. F. The formed package must be able to withstand the still relatively high temperatures of the food product immediately after packaging, and subsequent cooling operations to bring the package to room temperature or other desired temperature range.
The flexible material must also have sufficient abuse resistance to physical and mechanical abuse imposed by the entire form-fill-seal or other packaging system, and the subsequent abuse which the package may undergo during the distribution cycle.
Yet another requirement of packaging material, especially in form-fill-seal systems, is good heat sealability with respect to the transverse heat seals, which are typically subjected to loading forces from the introduced product such as food product, soon after the heat seal is formed.
Of interest in U.S. Pat. No. 4,284,674 issued to Sheptak and disclosing a multilayer film having a core layer of ethylene vinyl alcohol copolymer adhered on each side to nylon, each nylon layer in turn being adhered to a chemically modified polyolefin, and a further layer of primer material suitable to adher the modified polyolefin to an outer layer of polypropylene or other materials suitable for conveying toughness, flex-crack resistance and moisture barrier properties to the multi-ply film.
Also of interest in U.S. Pat. No. 4,355,721 issued to Knott et al and disclosing a coextruded multilayer sheet having a first layer of nylon, an EVOH barrier layer, another layer of nylon, and adhesive layer, and another outside layer of, for example, high density polyethylene.
Of interest is U.S. Pat. No. 4,398,635 issued to Hirt and disclosing a medication package in which a coextruded multiple layer sheet may have a structure including a layer of ethylene vinyl alcohol copolymer sandwiched between adjacent layers of nylon, and in which one of the nylon layers may be further adhered to a tie resin. The nylon layers may form either an outside surface or, in one example, internal layers with additional layers of polymeric materials added to each side of the sandwich structure.
Of interest is U.S. Pat. No. 4,407,873 issued to Christensen et al, disclosing a packaging material for retort applications including a heat seal layer of linear low density polyethylene, a second layer of linear low density polyethylene with optionally 0% to 80% medium density polyethylene blended into the second layer, a third layer of anhydride modified medium density polyethylene, a fourth layer of nylon, a fifth layer of ethylene vinyl alcohol copolymer, and a sixth layer of nylon.
Of interest is U.S. Pat. No. 4,457,960 issued to Newsome, disclosing a multilayer film having a core layer of a barrier material such as EVOH and EVOH blends. This film may be shrinkable and may be melt extruded, and may contain outside layers having a blend of linear low density polyethylene and ethylene vinyl acetate copolymer.
Of interest is U.S. Pat. No. 4,495,249 issued to Ohya et al, disclosing a five-layer film having a core layer of a saponified copolymer of ethylene and vinyl acetate, outer layers of a mixture of linear low density polyethylene and ethylene vinyl acetate copolymer, and two adhesive layers disposed between the core layer and outer layers.
It is an object of the present invention to provide a multilayer film suitable for the packaging of food products, especially high acid content food products at relatively high temperatures.
It is a further object of the present invention to provide a multilayer film useful in connection with form-fill-seal processes especially vertical form-fill-seal processes.
It is still another object of the present invention to provide a multilayer film which provides extended shelf like to food products such as high acid content food products.
It is yet another object of the present invention to provide a multilayer film which can be made into a package for food products which can be reheated in boiling water without delamination or breakage.
One particularly useful feature of this package is its usefulness in packaging food products currently packaged in metal packaging such as No. 10 metal cans. These cans tend to be expensive, bulky during shipment and, after use of the contained food product, difficult to dispose of. Utilizing the multilayer film of the present invention, many food products now packaged in the No. 10 can be conveniently and quickly packaged, stored, shipped, marketed, and sold to the end user such as a commercial or institutional user or a consumer. After use, the emptied package made from the multilayer film provides a much less bulky package for disposal.